I follow his advice of 3x15 roughly every other day on the harness work and such. Other than that, wrestling and muay thai clinch sparring (in both the neck is a major control point) will build a degree of strength into your neck

"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". - Cus D'Amato

laying back over a bench or gym ball reverse neck curls (weight on forehead) 3x15 you will need to use a much lower weight for these than the harness work

I alternate this in with bridge training in which case I do front and back bridges and headstands for 3x1min

I try to do it roughly every other day but 2-3 times a week is good enough imo.

"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". - Cus D'Amato

Neck weights add bridging can be dangerous if not done correctly, the easiest way to start strengthening you neck is doing neck ups, where you lie on you back, front and sides and lift your head up and down.

I found that doing side to side exercises resulted in my neck clicking and grinding alot more than normal in everyday life. So I would advise against them.

Tbh to begin with, as Odacon said, neck ups are a good way to build a bit of neck mass and strengthen your neck at least to the point that you can easily support your own head for increased periods. You would be surprised how many of you can't do more than a certain amont of crunches because your neck gives out befoe your abs.

"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". - Cus D'Amato

wrestlers bridges - Go up into the (no hands, have a look in the below video, the one I'm talking about here is progression #6, but without the rocking) bridge and hold position for 30 seconds. Rest for a minute. Repeat 3 times. As this gets easier increase the time. Do this twice a week.

During warm up for sambo we do progrssion #4 from the following video at 1:05. We also roll our heads from side to side from the same position:

Wrestling drills and Thai clinch drills are having a big impact in my neck strength. Just doing basic plum pummeling drills where you make sure you both keep your heads up straight when the person puts the clinch on are very good.

A nice simple exercise we do is neck raises ( like a sit up but only moving your head ). You lie on your back, arms at your sides, and you do like 50 neck raises then again while on your stomach. If your neck needs work you will really feel that one.